ECE 695Numerical Simulations

Lecture 37: Preparing for our Final Presentations

Prof. Peter Bermel

April 17, 2017

Program for Monday, April 24

Time Presenter Title

9:30 AM Sayan Roy Exploring Tungsten Trioxide (WO3) as a potential light-absorbing material for photovoltaic applications

9:40 AM David Kortge Modeling Photovoltaic Parameters as a Function of Lateral Doping Profile in Polycrystalline Absorber Layers

9:50 AM Evan Schlenker Thermal FEM Modeling with Experimental Optical Data Integration for Transient Laser Diode Characterization

10:00 AM Di Wang Numerical simulation of optical heating systems

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Sayan RoyExploring Tungsten Trioxide (WO3) as a potential light-

absorbing material for photovoltaic applications

There is a great deal of interest in light absorbing materials which can efficiently convert photons in sunlight to electron-hole pairs and generate electricity. Tungsten Trioxide (WO3) has been in use as a photocatalyst, where it becomes activated by incident sunlight and helps is speeding up a chemical reaction. It has significant light absorbing properties which can make it a suitable candidate for a photovoltaic material. In this work, I have explored the electronic properties of WO3, such as electronic band structure along with the bandgap, density of states and absorption coefficient, to understand its absorptive behavior, and explored the features which can make it a good photovoltaic material. First, the electronic band structure and bandgap was calculated by Density Function Theory (DFT) calculations followed by GW correction using the tool Quantum ESPRESSO. Using the DFT+GW results, the density of states and absorption coefficient were obtained, which gave a clear picture into its applicability as a photovoltaic material. This material was tested with different thicknesses to observe the impact of the thickness on its absorptive behavior. The configuration which gave the best performance was implemented in conjunction with a convention silicon solar cell to observe the improvements in the performance of the solar cell. The silicon solar cell was modified to include WO3 to enhance absorption of sunlight. A hybrid structure, similar to HIT solar cells (known to have high efficiencies), was created and explored under different configurations to obtain the optimum device with best performance parameters.

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David KortgeParticle Swarm Optimization to characterize

surface roughness for thin film silicon

A MATLAB code using Particle Swarm Optimization to model the surface roughness of a thin film selective absorber was created. Simulations of the selective absorber, when modeled with ideal flat surfaces, deviated from the experimental data. Using Particle Swarm Optimization (PSO) and emissivity data, the surface roughness of the thin silicon was simulated as the combination of silicon layers of varying thicknesses using weighting factors correlating to the fraction of the surface at that thickness to the overall height distribution. This surface distribution was then compared with Atomic Force Microscopy (AFM) data to determine accuracy of the simulation.

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Evan SchlenkerThermal FEM Modeling with Experimental Optical DataIntegration for Transient Laser Diode Characterization

Laser diodes have realized increased prominence in electronics, industrial manufacturing, and military applications. They present a unique interdisciplinary challenge of managing high thermal loads in the transient case to ensure that the desired optical and electrical characteristics are maintained. There has been little prior work relating thermal and optical characteristics of laser diodes, partly due to the difficulty of achieving reliable localized data. A 2D FEM model can be used in conjunction with measured optical and thermal data to overcome physical measurement limitations to enhance understanding and analysis of a laser diode system. A FEM model developed in FAESOR by Dan Konopa is modified and adjusted to accommodate novel cooling solutions and verified against experimental data.Comparing the modeled thermocouple temperatures with experimental values allows for extrapolation of the quantum well temperature, which cannot be readily measured with a thermocouple. Both individual node elements and collective temperature changes in the quantum well can be incorporated into laser diode physics equations and statistical analysis to glean information about the laser performance, including spectral shift.The 2D FEM model can be used to enhance understanding of a complex electrical/optical/thermal laser diode system. The model provides physically unattainable quantum well temperatures, which give information about diode performance. Obtaining this information from optical data can provide an easier route for system analysis.

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Di WangNumerical simulation of optical heating systems

Optically induced heating is the main channel of energy loss in many optical systems, thus are in general unwanted in applications requiring high optical quality factors. However, recently, there is a rapidly growing trend of research activities aiming to harness the optical heating effect. For example, in thermal photovoltaics (TPV), graphene photothermoelectric (PTE) detectors, heat assisted magnetic recording (HAMR), optofluidics studies and many more, carefully designed optical heating elements are desired to engineer the temperature profile in materials. Plasmonics has been proven to be a promising candidate for optical heating due to its ability to confine the electromagnetic energy into nanoscale volumes. Although there are numerous numerical tools for plasmonicsimulation, integrating plasmonic and thermal simulations correctly can be computationally challenging due to the large discrepancy in the dimensions of the two simulation domains. In this talk, I will talk about the method of separating the two simulation domains to achieve more accurate temperature profile results, and validate the method by comparing numerical results (COMSOL) against analytical result, and also against a published work. Because the separated method does not consider the heating configuration at nanoscale sizes, it is only valid in describing temperature profile at a relatively large scale. As will be shown, under specific simplifications and assumptions, the numerical result agrees with published work, and also matches very well with analytical result at describing the average temperature of the heated surface.

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Program for Wednesday, April 26

Time Presenter Title

9:30 AM Elizabeth Grubbs Multiprobe characterization analysis of direct bandgap semiconductors via PLE and EQE techniques

9:40 AM Allison Perna Modeling Photovoltaic Parameters as a Function of Lateral Doping Profile in Polycrystalline Absorber Layers

9:50 AM Hao Tian Optimization and analysis of multilayer anti-reflection coating for thin-film Si selective solar absorber

10:00 AM Oluseye Akomolede Analysis of the resonant frequencies and fundamental modes of arbitrarily shaped 3D resonant cavities

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Elizabeth GrubbsMultiprobe characterization analysis of direct bandgap

semiconductors via Photoluminescent Excitation Spectroscopy and External Quantum Efficiency techniques

Material selection is a critical step in the design of an effective and efficient electronic device, for photovoltaic (PV) or traditional electronic applications such as LEDS or high power electronics. Often times these materials are not silicon and have less established quantitative values for parameters such as surface recombination velocities as well as bulk lifetimes. Furthermore, their numerical value as well as their dependence on wavelength can be nontrivial and multiple methods of characterization are needed to extrapolate their behavior. Photoluminescence Excitation Spectroscopy (PLE) and External Quantum Efficiency measurements (EQE) are two different characterization techniques that, depending on the material and its quality, may or may not have similar data curves. Simulating different samples such as GaAs and other direct band gap materials in Sentaurus and their resulting PLE and EQE signals yields insight into how the two techniques produce data of similar forms for some samples and drastically different for others. The degree of matching between the EQE and PLE data is largely controlled by the sample quality or in the case of the GaAs samples, the quality of the substrates.

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Allison PernaModeling Photovoltaic Parameters as a Function of Lateral

Doping Profile in Polycrystalline Absorber Layers

Semiconductor materials are known to exhibit inhomogeneous dopant profiles. While industry doping methods such as ion implantation commonly create vertical variation in dopant concentration, lateral inhomogeneities can be inadvertently realized as well with other methods. Introduction of dopants as gaseous precursors during materials growth or spin-coating of dopants may, in combination with a polycrystalline growth process, cause variation in the lateral dopant profile. We model this behavior in 2D using drift-diffusion models and SENTAURUS, a finite-element modeling program, specifically with InP absorber layers grown via the thin-film vapor-liquid-solid (TF-VLS) method. Variation in local VOC from 690 to 780 mV inferred from photoluminescence images of this material supports potential variation in local dopant concentration, potentially within each grain and across grains. This project uniquely investigates various periodic dopant profiles within grains; sample-wide dopant profiles are investigated as well. Semiconductor and specifically photovoltaic parameters are modeled for comparison with experimental results. This work provides fundamentals for investigation into lateral dopant profiles of other materials systems.

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Hao TianOptimization and analysis of multilayer anti-reflection coating

for thin-film Si selective solar absorber

To increase the absorption of the thin film selective solar absorber, multilayer anti-reflection coating is designed and optimized, which consists a layer of SiO2 followed by TiO2. Local optimization is performed for 20 um Si and at 550C. The optimal thicknesses for SiO2 and TiO2 are found to be 100nm and 50nm respectively, which yields 76.59% thermal transfer efficiency at 100 suns concentration. The selective absorber exhibits sharp selectivity and flat absorptivity below cutoff wavelength which is around 97% from 400nm to 1100nm. The influence of temperature is also analyzed for 20 um Si. The optimal operation temperature is around 450C at high concentration, and it gradually decreases as the concentration decreases. Finally, the dependence of efficiency on Si thickness is examined under 550C. The optimal Si thickness decreases as we decrease the concentration. In conclusion, the two-layer anti-reflection coating (SiO2+TiO2) design increases the absorption of the selective absorber as compared with one-layer design (Si3N4), while having little influence on the thermal re-radiation. Therefore, this structure produces higher thermal transfer efficiency, and in the same time, is simple and easy to fabricate.

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Oluseye AkomoledeAnalysis of the resonant frequencies and fundamental modes of

arbitrarily shaped 3D resonant cavities

In this presentation, the analysis of the resonant frequencies and fundamental modes of arbitrarily shaped resonant cavities in three dimensions is explored. An incremental insertion Delaunay triangulation algorithm, a medial axis calculation algorithm, an algorithm for meshing the interior of a domain based on the medial axis, and a fast, GPU-based finite element method algorithm were employed to facilitate the exploration. The agreement of results obtained with analytical solutions, as well as the peculiar behavior of selected cavities is demonstrated.

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Program for Friday, April 28

Time Presenter Title

9:30 AM Samik Mukherjee Coupled Electro Thermal Optical Simulation of III-Nitride Multi-Quantum Well LEDs

9:40 AM Keith McKinzie Simulation of Fano Laser Self-Pulsation Physics and Coherence

9:50 AM Shuhui Tang Transfer Matrix and finite element model method for Surface acoustic wave delay line band pass characteristics

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Samik MukherjeeCoupled Electro Thermal Optical Simulation of III-

Nitride Multi-Quantum Well LEDsWide band gap materials like III-Nitrides have gained wide-spread popularity for emitting in blue wavelength. These materials find applications in multi-quantum well LEDs and Quantum Cascade Lasers. High quality LEDs are grown by Molecular Beam Epitaxy techniques with precise control of material parameters and dimensions. Since, such precise control is available, optimization of structures with simulation methods are need of the hour to design highly efficient LEDs with very high quantum efficiency. There is a plethora of simulation tools available for simulation of electrical, optical and thermal simulations. Starting from electrical simulations ranging from drift-diffusion there are more sophisticated models such as Boltzmann transport equation for non-equilibrium carrier dynamics and Non-Equilibrium Green’s function based quantum transport models. Similarly for optical simulation there are also a plethora of tools available from simple ray tracing geometrical optics to more sophisticated ones such as FDTD. Thermal simulations also begin with the most simple ubiquitous heat equation, to more sophisticated ones with Boltzman transport equation and Phonon transport models. Although each of them give results with varying sense of accuracy, one of the most over-looked aspects is that all three of these simulations are connected , and one has solve a coupled model. The parts of the device that lead to non-radiative recombination dissipate heat with a change of lattice temperature in these parts. Obviously a change in lattice temperature would lead to a different recombination-generation rate of carriers and change in scattering rate of carriers, both of which changes I-V curves and output optical power. Again only a part of radiative recombination is output from the device, which depends on the external quantum efficiency. The rest of this output radiation is self-absorbed in the same device leading to heating, which can be described by a simple attenuation constant. Moreover, if one wishes to do a more accurate electron transport analysis of I-V curves, one needs to consider how a strong radiation changes quantized levels in the quantum well regions by quantum confined stark effect. Furthermore external quantum efficiency also changes with strong radiation strength due to optical non-linearity such as kerr and pockel effects. This discussion may make one realise that it is important for one to couple electrical , thermal and optical effects for a realistic quantitative LED simulation. In our model we shall describe electronic transport by drift diffusion , temperature variation by heat equation and the effect of optical radiation by an attenuation constant. We will study how these effects change when coupled together , effects current , output light intensity and temperature variation , w.r.t uncoupled models.

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Keith McKinzieSimulation of Fano Laser Self-Pulsation Physics and

CoherenceDue to a drive for portable optical clocks, spectroscopic laser sources, and optical taps for wavelength division multiplexing communications and RF photonics.Due to this drive, many different integrated optical pulse sources have been pursued, including microring resonators, modulated discrete mode diode lasers, and compact electro-optic sources are a few examples of promising integrated optical sources. In May of 2016, Yi Yu showed a self-pulsation spanning up to 10GHz. The laser’s pulsing behavior was due to absorption of un-pumped quantum dot behavior in the high Q factor Fano resonance, causing the laser to behave as a saturable absorber. The paper did some brief studies, but did not attempt to optimize laser pulsing, giving a noising frequency comb output. Here I investigate the effect of changing coupling of the side resonance, and engineering the line-defect photonic crystal laser cavity dispersion, to minimize the measured RF linewidth of a photodetectedoutput pulse train.

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Shuhui TangTransfer Matrix and finite element model method for

Surface acoustic wave delay line band pass characteristics

Surface acoustic wave can be generated by exciting electrical signal in interdigital transducer(idt) on piezoelectric material. The wave can travel along the surface and be picked up by another set of idts to be converted back to electrical signals. They have been used as transmission line, wake up circuit, and filters because how sensitive and how power efficient they are. However, the effects of how the idt features affect the band pass characteristics characteristic including the center frequency, bandwith, and insertion loss of the SAW device are not that clear. Therefore a GaN on SiC substrate device with two pairs of idts that simulate a delay line are examined in the simulation. This simulation uses finite element anlysis and transfer matrix to understand the relationship between the input and output voltage and how the idt features affect the band pass characteristics and frequency response.

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Recommended Outline

• Slide 1: Title Slide

• Slides 2-3: Problem Description

• Slides 4-5: Mathematical Model Formulation

• Slides 6-7: Proposed Problem Solution

• Slides 8-10: Problem Solution Implementation

• Slides 11-12: Results and Conclusions

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Slides 2-3: Grading

Unsatisfactory (0-3) Needs

Improvement (3-5)

Meets Expectation

(5-8)

Exceeds Expectation

(9-10)

Problem Description and Abstract

(20%)

Describe the problem that is

proposed to be solved and

provide a justification using

literature from relevant research

papers.

An unclear

description of the

problem statement

and no relevant

research backing

provided.

Description of the

problem statement

needs refinement.

Inadequate

research relevance.

The problem is

defined

appropriately, but

will need a little

more refinement in

terms of relevant

literature.

The problem is very

well defined, and the

literature from

relevant research

work builds a

persuasive case for

the problem.

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Slides 4-5: Grading

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Unsatisfactory(0-3) Needs Improvement

(3-5)

Meets Expectation

(5-8)

Exceeds Expectation

(9-10)

Problem Framing

Analytical (10%)

Numerical (10%)

Build both analytical and

numerical models to help solve the

problem.

Interpret the problem (goals,

information, limitations, and

assumptions) in terms of relevant

models, concepts or theories.

-No analytical or

mathematical

model included in

the report.

- An analytical and

mathematical model is

provided, but it is

incorrect.

- An analytical model

is provided, but

needs minor

improvisation.

- A mathematical

model is provided,

but needs minor

improvisation.

-Both the analytical

and mathematical

models provided

accurately frame the

problem.

18

Slides 6-7: Grading

Unsatisfactory(0-3) Needs Improvement (3-

5)

Meets Expectation (5-

8)

Exceeds Expectation

(9-10)

Problem Synthesis

Define and Build (15%)

Validate (10%)

Evaluates the quality of the solution

approach built to solve the problem.

The simulation needs to be validated

thoroughly with either experimental

data or test cases. Predictively

compare and contrast alternate

solution processes in terms of

relevant metrics (e.g., accuracy,

computational time, etc.). Develop a

simulation (potentially built on an

existing platform like MEEP) to solve

the problem.

-The

implementation of

the solution

approach is

incorrect.

-The solution

approach is not

validated

-The implementation of

the solution approach

serves the purpose, but

needs refinement.

-The validation process

for the solution

approach needs to be

improved.

-The implementation

of the solution

approach provides the

approach to solve the

problem, but needs

minor improvements.

-The validation process

for the solution

approach needs minor

improvements,

-The implementation

of the solution

approach is accurate.

- The solution

approach is validated

appropriately.

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Slides 8-10: Grading

4/17/2017 ECE 695, Prof. Bermel

Unsatisfactory(0-

3)

Needs Improvement

(3-5)

Meets Expectation

(5-8)

Exceeds

Expectation (9-10)

Problem Implementation and

Solution

(30%)

Evaluates whether the student

can use the model they build

to solve the problem in a

satisfactory and convincing

fashion.

Can this code help solve

significant research problems

of current interest?

-No solution

provided to the

problem.

-Does not discuss

the application of

solution for a

related problem.

- A solution is

provided, but it is

incorrect or does

not adequately

address the issue or

problem.

-Not a clear

description of how

the solution can be

used to resolve a

related problem.

-A solution is

provided that

would adequately

address the issue or

problem, but it is

presented in a way

that is unclear, or

improperly

documented.

-A discussion is

included which

describes the use of

the current

approach to solve

related problems.

- A solution is

provided that is

correct, clear and

well documented.

-A very clear

explanation is

provided of how

the current

approach can help

solve related

problems of

interest.

20

Slides 11-12: Grading

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Unsatisfactory

(0-3)

Needs

Improvement (3-5)

Meets

Expectation (5-8)

Exceeds

Expectation (9-10)

Organization of the

Presentation (5%)

An important aspect of a

project report is its clarity

to the audience, as well

as the professional nature

of its presentation.

Presentation is

highly unclear

and

unprofessional.

Presentation has a

number of unclear

or unprofessional

problems.

The presentation

is mostly clear,

but has 5 or

fewer minor

points of

confusion.

The presentation is

highly clear, and

has

21

All the above, plus…

Extra Credit Opportunity

• Fill out the course survey before it closes, and send me a screenshot with the proof

• Will replace your lowest HW score in the final grade with a 100

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Next Class

• Note that there’s no class this Wednesday & Friday (Apr. 19 & 21)

• We will meet next on Monday, April 24 to kick off our initial final project presentations!

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